The present invention relates to a thermoplastic film containing a core layer and an enhanced printing skin layer. The core layer comprises an orientation-enhancing polymer, a polypropylene homopolymer, a beta-crystal nucleators of polypropylene, and optionally a water absorption additive. The thermoplastic film is an oriented film and may be opaque.
Water based ink printing on standard thermoplastic polypropylene film requires a long time to dry. This is a particular problem when standard thermoplastic polypropylene films are used with ink-jet printing. Additionally, for good adhesion when using films with water-based pressure sensitive adhesives or with cold glues, good drying and adhesion properties are desired. Further, breathable films with good water vapor transmission are desired for bags, absorbent articles and garments.
Park et al, U.S. Pat. No. 4,632,869, discloses an opaque, biaxially oriented film structure having a polymer matrix with strata of cavitated voids, in which the voids contain spherical void-initiating particles of polybutylene terephthalate (PBT). The structure may also include thermoplastic skin layers, and the film can also include pigments such as TiO2 or colored oxides.
Park et al, U.S. Pat. No. 4,758,462, discloses an opaque, biaxially oriented film with a cavitated core layer and transparent skin layers. Colored light absorbing pigments such as carbon black or iron oxide are added to the core and/or the skins to decrease light transmission through the film.
Crass et al, U.S. Pat. No. 4,652,489 discloses an oriented, sealable, opaque polyolefin multi-layer film with a core layer containing vacuoles or voids, a sealable surface layer, and a non-sealable surface layer which incorporates a slip agent such as a polydiorganosiloxane.
Amon et al, U.S. Pat. No. 6,194,060, discloses an opaque, oriented polymeric film structure, suitable for food packaging, comprising: (a) a core layer containing a thermoplastic polymeric matrix material which has a first surface and a second surface, the core layer having a plurality of voids, substantially all or all of the voids being free from a void-initiating particle and at least some of the voids being interconnected with an adjacent void in the polymeric matrix material, the number of voids not containing a void-initiating particle being sufficient to impart a significant degree of opacity to the film structure; and (b) at least one outer or skin layer containing a thermoplastic polymeric material and an effective amount of a nucleating agent to suppress cavitation in said at least one outer or skin layer. The film structure is stated to have a smooth surface and to be tailorable to provide a controlled permeability.
Amon et al, U.S. Pat. No. 6,303,233, discloses a uniaxially heat-shrinkable, biaxially oriented, multilayer film having a polypropylene-containing core layer containing at least 70 wt. % of the multilayer film and at least one polyolefin-containing skin layer adjacent the core layer, which is prepared by biaxially orienting a coextrudate and thereafter orienting the coextrudate by stretching 10 to 40% in the machine direction. The core layer contains isotactic polypropylene, a modifier which reduces the crystallinity of the polypropylene-containing core layer and a nucleating agent. The modifiers include atactic polypropylene, syndiotactic polypropylene, ethylene-propylene copolymer, propylene-butene-1 copolymer, ethylene-propylene-butene-1 terpolymer, and linear low density polyethylene. The nucleating agent is said to improve long term dimensional stability. The skin layer can be high density polyethylene on both sides or high density polyethylene on one side and isotactic polypropylene on the other side.
Amon, U.S. Pat. No. 6,183,856, discloses a process for forming film structures which have a plurality of voids, at least some of the voids not containing a void-initiating particle and at least some of the voids being interconnected with an adjacent void in the polymeric matrix material, with the number of voids being sufficient to impart a significant degree of opacity in the film structure.
Davidson et al, EP0865909, discloses biaxially oriented heat shrinkable polyolefin films for use as labels, having a layer of a polypropylene-based resin with microvoids therein. The microvoids having been formed by stretching a web containing the beta form of polypropylene.
Davidson et al, EP0865910, and Davidson et al, EP0865912, disclose biaxially oriented polyolefin opaque films having a thickness of not more than 50 xcexcm having a layer of a polypropylene-based resin with microvoids therein. The microvoids having been formed by stretching a web containing the beta form of polypropylene at an area stretch ration of at least 15:1.
Davidson et al, EP0865911, discloses biaxially oriented polyolefin films, including microvoids formed by stretching polypropylene based resin which contains the beta form of polypropylene, and a heat seal layer. The heat seal becomes transparent upon heating.
Davidson et al, EP0865913, discloses biaxially oriented heat shrinkable polyolefin films having a layer of a polypropylene-based resin with microvoids therein. The microvoids having been formed by stretching a web containing the beta form of polypropylene, the film having a shrinkage after 10 minutes at 130xc2x0 C. of at least 10% in at least one direction.
Davidson et al, EP0865914, discloses biaxially oriented high gloss polyolefin films having a layer of a polypropylene-based resin with microvoids therein and at least one olefin copolymer outer layer thereon. The microvoids having been formed by stretching a web containing the beta form of polypropylene.
Jacoby et al, U.S. Pat. No. 5,594,070 discloses oriented microporous films prepared from polyolefin resin compositions comprising an ethylene-propylene block copolymer having an ethylene content of about 10 to about 50 wt. %, a propylene homopolymer or random propylene copolymer having up to about 10 wt. % of a comonomer of ethylene or an xcex1-olefin of 4 to 8 carbon atoms, and components selected from a low molecular weight polypropylene, a beta-spherulite nucleating agent and an inorganic filler. The microporous films are said to have improved breathability, strength, toughness and break elongation. However, the films of Jacoby have a tendency to exhibit pink color when red dye (beta-spherulite nucleating agent) concentration is higher than 50 ppm. If the concentration of red dye (beta-spherulite nucleating agent) is lower than 50 ppm, then it is difficult to obtain consistent opacity due to poor dispersion uniformity.
Jacoby et al, U.S. Pat. No. 5,310,584, discloses a thermoformable sheet comprising a resinous polymer of propylene and an effective amount of a beta-spherulite nucleating agent, a process for making the sheet and articles thermoformed from the sheet.
Xu et al, U.S. Pat. No. 5,134,174, discloses polypropylene microporous films having a porosity of 30-35%, an average pore size of 200-800 xc3x85, a permeation coefficient for nitrogen of 1-5xc3x9710xe2x88x923 ml/cm sec atm and a tensile strength of greater than 60 MPA in all directions within the film plane. The films are prepared by the consecutive steps of biaxial stretching a non-porous starting film of high beta-crystal content and heat setting the stretched film.
Kobylivker et al, U.S. Pat. No. 6,072,005 discloses a breathable film, having certain physical and barrier properties, made from a stretched impact modified polyolefin matrix and a particulate filler. The impact modified polyolefin matrix includes at least one impact polypropylene copolymer, alone or in combination with other polymers. The film, and laminates including the film, are stated to provide moisture breathability and barrier to penetration by liquids. Disclosed uses for laminates including the film include diaper outercovers and other applications requiring breathability and resistance to penetration by liquids.
Water based ink printing on standard thermoplastic polypropylene film requires a long time to dry. This is a particular problem when standard thermoplastic polypropylene film are used with ink-jet printing. The film of the present invention provides for superior water absorption and is particularly effective for water-based printing. Further, the film of the present invention shows good drying due to good water vapor permeability when it is used with a water-based pressure sensitive adhesive or with a cold glue as a label. Another advantage is when the film of the present invention is used as a label with a pressure sensitive adhesive, due to the paper tear property, the film of the present invention may be used as evidence of tampering. Thus, the film of the present invention may be used as a tamper evident label, for water-based ink printing applications, for ink-jet printing and as a synthetic paper. In addition to water based inks, the film of the present invention may also be used as a printable surface for solvent based inks and UV-curable inks.
The film may also be used in applications where breathable films are employed and good water vapor transmission are desired. For example as a backsheet component in a personal care absorbent article, such as a diapers, training pants, incontinence garments, feminine hygiene products and the like. The relative humidity and temperature within the diaper or other product can be reduced by using breathable films and laminates. The film may be used as a cover or bag for produce. The film may also be used in surgical gowns, protective workwear, wound dressings and bandages, where an objective is to provide good water vapor transmission and make the item more comfortable to the wearer.
The opaque film of the present invention is different from the conventional opaque polypropylene films. Conventional opaque polypropylene films are cavitated by organic polymers or inorganic fillers.
In the present invention, beta-crystal growth during polypropylene film casting is controlled, followed by orientation, to create the high permeability opaque film.